Use srcset's resource pixel density to determine intrinsic size

Source/core/rendering/RenderImage.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2006 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 43 matching lines @@
     void areaElementFocusChanged(HTMLAreaElement*);
 
     void highQualityRepaintTimerFired(Timer<RenderImage>*);
 
     void setIsGeneratedContent(bool generated = true) { m_isGeneratedContent = generated; }
 
     bool isGeneratedContent() const { return m_isGeneratedContent; }
 
     String altText() const { return m_altText; }
 
+    inline void setIntrinsicSizeFactor(float factor) { m_intrinsicSizeFactor = factor; }
+    virtual LayoutSize intrinsicSize() const OVERRIDE;
+    LayoutSize unscaledIntrinsicSize() const;

[pdr., 2013/10/11 05:17:33]

Can we change this to something more descriptive? Possibly
"intrinsicSizeWithoutSrcsetDevicePixelRatio()"?
Similarly for the intrinsicSizeFactor. Possibly "m_srcsetDevicePixelRatio" and
"setSrcsetDevicePixelRatio(...)"?
Similarly for HTMLImageElement, etc.

This sounds pedantic but there are already several scale factors (ctm scale,
screen's device pixel ratio, page zoom scale) and it sounds like we're even
going to add another device pixel ratio soon (for client hints).

[Yoav Weiss, 2013/10/11 07:22:32]

I think (hope) this mechanism is not srcset specific, and CH, image-set and srcN
could use it just as well.

Maybe intrinsicSizeWithoutDevicePixelRatio() ?

 protected:
     virtual bool needsPreferredWidthsRecalculation() const OVERRIDE FINAL;
     virtual RenderBox* embeddedContentBox() const OVERRIDE FINAL;
     virtual void computeIntrinsicRatioInformation(FloatSize& intrinsicSize, double& intrinsicRatio, bool& isPercentageIntrinsicSize) const OVERRIDE FINAL;
 
     virtual void styleDidChange(StyleDifference, const RenderStyle*) OVERRIDE FINAL;
 
     virtual void imageChanged(WrappedImagePtr, const IntRect* = 0);
 
     void paintIntoRect(GraphicsContext*, const LayoutRect&);
@@ skipping 20 matching lines @@
     virtual LayoutUnit minimumReplacedHeight() const OVERRIDE;
 
     virtual void notifyFinished(Resource*) OVERRIDE FINAL;
     virtual bool nodeAtPoint(const HitTestRequest&, HitTestResult&, const HitTestLocation& locationInContainer, const LayoutPoint& accumulatedOffset, HitTestAction) OVERRIDE FINAL;
 
     virtual bool boxShadowShouldBeAppliedToBackground(BackgroundBleedAvoidance, InlineFlowBox*) const OVERRIDE FINAL;
 
     IntSize imageSizeForError(ImageResource*) const;
     void imageDimensionsChanged(bool imageSizeChanged, const IntRect* = 0);
     bool updateIntrinsicSizeIfNeeded(const LayoutSize&, bool imageSizeChanged);
+    virtual float intrinsicSizeFactor() const { return m_intrinsicSizeFactor; }
     // Update the size of the image to be rendered. Object-fit may cause this to be different from the CSS box's content rect.
     void updateInnerContentRect();
 
     void paintAreaElementFocusRing(PaintInfo&);
 
     // Text to display as long as the image isn't available.
     String m_altText;
     OwnPtr<RenderImageResource> m_imageResource;
     bool m_needsToSetSizeForAltText;
     bool m_didIncrementVisuallyNonEmptyPixelCount;
     bool m_isGeneratedContent;
+    float m_intrinsicSizeFactor;
 
     friend class RenderImageScaleObserver;
 };
 
 inline RenderImage* toRenderImage(RenderObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderImage());
     return static_cast<RenderImage*>(object);
 }
 
 inline const RenderImage* toRenderImage(const RenderObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderImage());
     return static_cast<const RenderImage*>(object);
 }
 
 // This will catch anyone doing an unnecessary cast.
 void toRenderImage(const RenderImage*);
 
 } // namespace WebCore
 
 #endif // RenderImage_h